High efficiency perovskite LED developed by Ningbo Institute of Materials, Chinese Academy of Sciences

Recently, the team of advanced nano optoelectronic materials and devices of the Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, took the lead in developing a highly efficient and stable perovskite light-emitting diode (LED) with world leading performance, which fundamentally clarified the source of instability of perovskite materials, solved the problem of operating stability of perovskite light-emitting diodes that has been puzzling them since their birth, and pointed out the direction for the industrialization of perovskite materials in the field of light-emitting displays.

  Perovskite materials are a type of material with the same crystal structure as natural calcium titanate ore (mainly composed of CaTiO3), and are currently one of the most promising optoelectronic materials with excellent optoelectronic properties and low preparation costs. Compared with existing organic light-emitting diode (OLED) technology, perovskite light-emitting diodes have narrower emission spectra and better color purity, which can meet the requirements of the next generation high-definition display technology Rec.2020 international standard and greatly improve the viewing experience for viewers. Therefore, perovskite is considered one of the most powerful competitors for next-generation luminescent display technology. However, despite significant progress in the efficiency of perovskite light-emitting diodes over the long term, the problem of low operational stability remains a major obstacle to the practical application of perovskite light-emitting diodes, especially with limited understanding of the fundamental sources that cause instability in perovskite materials. This undoubtedly hinders the further improvement of the performance and commercialization process of perovskite light-emitting diodes.

  Therefore, the advanced nano optoelectronic materials and device team of Ningbo Institute of Materials, starting from luminescence display, focused on the key scientific issue of the instability source of perovskite materials, and conducted in-depth analysis of the fine nanostructure inside representative quasi two-dimensional perovskite materials. Finally, it was determined that the thinner nanosheet like structure inside perovskite (only one to two layers of lead ions) is the key source of inducing perovskite instability. The formation of these thinner nanosheet structures is due to rapid and uncontrollable crystallization processes, which have poor crystallization quality, numerous defects, and are prone to decomposition; Moreover, their decomposition will further induce the decomposition of the entire perovskite film, greatly reducing the overall stability of perovskite materials. Therefore, it is necessary to develop effective methods for accurately removing these thin nanosheets. Unfortunately, due to the nanoscale of thin nanosheets and their close stacking with other structures, the difficulty of removing these thin nanosheets is no less than accurately removing leaves of a specific shape from vast forests, and traditional macroscopic processing methods are difficult to achieve.

  To solve this problem, the team was inspired by the process of using a sieve to screen sand particles of different sizes and creatively developed the "solvent sieve" method, which achieved precise screening of nanosheets of different thicknesses, effectively removing thin nanosheets, and greatly improving the stability and luminescence performance of the final perovskite material. The solvent sieve developed by the team is a combination of polar and non-polar solvents. Just as we can control the size of sand particles passing through the sieve by adjusting the size of the mesh on the sieve, the research team utilizes the characteristic that thinner nanosheets have higher solubility in polar solvents than other components. By precisely adjusting the proportion of polar solvents, the intensity of the screening process is adjusted to only dissolve thin nanosheets with one to two layers of lead ions, without harming other structures in perovskite materials, The effect is shown in the figure. This method not only significantly improves the luminescent performance and stability of perovskite materials, but also greatly expands the toolbox for manipulating the fine nanostructure of perovskite, paving the way for the future development of perovskite materials with unique nanostructures and excellent luminescent properties.

  After removing the thin nanosheets through the "solvent sieve" method, the perovskite material exhibits astonishing stability. Not only can it maintain its luminescent performance in humid air for more than 100 days, but the prepared perovskite light-emitting diode also exhibits an operating life of over 50000 hours (5.7 years) under conventional usage conditions (100 cd/m2 brightness), which is nearly 30 times longer than before treatment. This operating lifespan is currently the highest among all green perovskite light-emitting diodes, meeting the requirements for commercial application. At the same time, the external quantum efficiency of perovskite light-emitting diodes also exceeds 29.5%, which is a record of the efficiency of perovskite light-emitting diodes designed without light extraction, significantly improving the efficiency of electrical conversion to light and simplifying the requirements of heat dissipation design. This research result undoubtedly lays a solid foundation for the application of perovskite materials in the field of luminescent displays, accelerating the process of perovskite luminescent display devices entering millions of households.